In general, linear motors are construction units suitable for comprehensive applications in automation. Conventional linear motors are often used in large units, in connection with construction of machines and semiconductor assembly. However, conventional linear motors are too large and too expensive to be used in applications such as laboratory automation, parts handling, optical testing technology, and the like. Thus, there is a need for compact and highly integrated linear motors provided with directly driven linear axes or tables and flexible fastenings.
While it is beneficial to manufacture linear motors provided with directly driven linear axes as inexpensively as possible, maintaining a high dimensional accuracy of the directly driven linear axes is important. The method accuracy of a linear motor's travel plate is generally determined by the position measurement system and the activation of the motor, and the dimensional accuracy of a linear motor is mainly affected by the guidance of the linear motor's travel plate.
Linear motors known in the art are usually provided with linear axes and compound tables. These linear motors, as disclosed in U.S. Patent Publication No. 20020140296A1, generally comprise a base plate, which is essentially a plane, a table plate movably held above the base plate, and a guiding and positioning means arranged between the base and table plates. Other linear motors known in the art are provided with analogous corresponding linear tables, as described in Japanese Patent Publication No. 2004188566A2. The above-mentioned linear motors may also be provided with guiding systems, such as rail or roller systems, which are arranged between the base and table plates. The guiding systems are usually designed as separate and pre-manufactured units and may be installed as finished elements on the linear motors. These guiding systems usually comprise two stable, precise rails, wherein roller cages or ball cages are held between the two rails. The fastening means between the base plate, the guiding system, and the travel plate of these linear motors are usually constructed very rigidly and precisely in order to provide exact guidance within the linear motors. This type of construction also allows the rails of the guiding systems, which is generally constructed of hard metals such as steel, to achieve the demanded precision and prevent wear of the rails.
In still another type of linear motors known in the art, in order to achieve high dynamics in the linear motors, the movable travel plate may be constructed with a lightweight metal, so that the mass of the travel plate is very low. However, the combination of the travel plate constructed of lightweight metal and the steel guide rails are limited in providing precise linear axes in the linear motors, because the coefficient of thermal expansion of steel and the lightweight metal are very different. Particularly, this limitation is commonly found in linear motors provided with integrated direct drives, which can cause the linear motor to heat up during operation. The heat can lead to various expansions of the metals, which in some cases, can lead to jamming of the guiding system.
Furthermore, some of these linear motors, due to the side surfaces of the linear motors and the arrangement of the base and travel plates, coupled with the intermediate arrangement of the respectively required rails, may not be suitable for use in some assembly systems. A solution to this limitation has been suggested in PCT Publication No. W002060641A1, which discloses a linear table comprising a base plate and side walls manufactured from a mono-block. However, the linear table is moved by way of a traction system, and the actual drive is not arranged between the two rails and the base plate and travel plate.